Reciprocal pilferage and the evolution of food-hoarding behavior

Current theories of food-hoarding behavior maintain that hoardingcan be adaptive if a hoarder is more likely than any other animalto retrieve its own caches. A survey of the literature indicatedthat the hoarder often has a recovery advantage when searchingfor items it has stored, but levels of cache pilferage are oftenso high (2–30% per day) that at least for some long-termfood hoarders, the caching animal is unlikely to recover a significantamount of its stored food. Except in a few cases (acorn woodpeckersand beavers), kin selection cannot explain the high levels ofpilferage observed. We suggest that some small solitary animalswith overlapping home ranges (e.g., most rodents, chickadees,and tits) are able to tolerate high levels of cache pilferage.Pilferage is not as damaging to these animals as it might otherwisebe because many interspecific and all intraspecific cache pilferersalso cache food. These or similar food caches can be pilferedlater by the original food hoarder. In other words, pilferingin these species is often reciprocal, and because it is reciprocal,it can be tolerated. We argue that caching systems based onreciprocal pilfering can be stable and are not necessarily susceptibleto "cheaters," animals that pilfer food but do not scatter hoardfood themselves, and we introduce a model of food hoarding tosupport this argument. These food-caching systems based on reciprocalpilfering resemble cooperative behavior, but the behavior isactually driven by the selfish interests of individuals. Thistheory of scatter-hoarding behavior based on reciprocity hasimportant implications for the ways that food-hoarding animalsinteract with inter- and intraspecific competitors.     

Acute rejection is associated with antibodies to non-Gal antigens in baboons using Gal-knockout pig kidneys

We transplanted kidneys from alpha1,3-galactosyltransferase knockout (GalT-KO) pigs into six baboons using two different immunosuppressive regimens, but most of the baboons died from severe acute humoral xenograft rejection. Circulating induced antibodies to non-Gal antigens were markedly elevated at rejection, which mediated strong complement-dependent cytotoxicity against GalT-KO porcine target cells. These data suggest that antibodies to non-Gal antigens will present an additional barrier to transplantation of organs from GalT-KO pigs to humans.     

Early responses to mechanical load in tendon: role for calcium signaling, gap junctions and intercellular communication

Tendon and other connective tissue cells are subjected to diverse mechanical loads during daily activities. Thus, fluid flow, strain, shear and combinations of these stimuli activate mechanotransduction pathways that modulate tissue maintenance, repair and pathology. Early mechanotransduction events include calcium (Ca2+) signaling and intercellular communication. These responses are mediated through multiple mechanisms involving stretch-activated channels, voltage-activated channels such as Ca(v)1, purinoceptors, adrenoceptors, ryanodine receptor-mediated Ca2+ release, gap junctions and connexin hemichannels. Calcium, diacylglycerol, inositol (1,4,5)-trisphosphate, nucleotides and nucleosides play intracellular and/or extracellular signaling roles in these pathways. In addition, responses to mechanical loads in tendon cells vary among species, tendon type, anatomic location, loading conditions and other factors. This review includes a synopsis of the immediate responses to mechanical loading in connective tissue cells, particularly tenocytes. These responses involve Ca2+ signaling, gap junctions and intercellular communication.     

Gene capture prediction and overlap estimation in EST sequencing from one or multiple libraries

Background  

In expressed sequence tag (EST) sequencing, we are often interested in how many genes we can capture in an EST sample of a targeted size. This information provides insights to sequencing efficiency in experimental design, as well as clues to the diversity of expressed genes in the tissue from which the library was constructed.     

Split tolerance in a novel transgenic model of autoimmune myasthenia gravis

Because it is one of the few autoimmune disorders in which the target autoantigen has been definitively identified, myasthenia gravis (MG) provides a unique opportunity for testing basic concepts of immune tolerance. In most MG patients, Abs against the acetylcholine receptors (AChR) at the neuromuscular junction can be readily identified and have been directly shown to cause muscle weakness. T cells have also been implicated and appear to play a role in regulating the pathogenic B cells. A murine MG model, generated by immunizing mice with heterologous AChR from the electric fish Torpedo californica, has been used extensively. In these animals, Abs cross-react with murine AChR; however, the T cells do not. Thus, to study tolerance to AChR, a transgenic mouse model was generated in which the immunodominant Torpedo AChR (T-AChR) alpha subunit is expressed in appropriate tissues. Upon immunization, these mice showed greatly reduced T cell responses to T-AChR and the immunodominant alpha-chain peptide. Limiting dilution assays suggest the likely mechanism of tolerance is deletion or anergy. Despite this tolerance, immunization with intact T-AChR induced anti-AChR Abs, including Abs against the alpha subunit, and the incidence of MG-like symptoms was similar to that of wild-type animals. Furthermore, evidence suggests that this B cell response to the alpha-chain receives help from T cells directed against the other AChR polypeptides (beta, gamma, or delta). This model offers a novel opportunity to elucidate mechanisms of tolerance regulation to muscle AChR and to clarify the role of T cells in MG.     

Changes in mass and energy transfer between the canopy and the atmosphere: model development and testing with a free-air CO2 enrichment (FACE) experiment

The rationale for this study is found in the probable higher temperatures and changes in rainfall patterns that are expected in the future as a result of increasing levels of CO2 in the atmosphere. In particular, higher air temperatures may cause an increase in evapotranspiration demand while a reduction in rainfall could increase the severity and duration of drought in arid and semi-arid regions. Representation of the water transfer scheme includes water uptake by roots and the interaction between evapotranspiration and CO2 enrichment. The predicted response of a spring wheat (Triticum aestivum L. cv. Yecora rojo) canopy in terms of energy exchange processes to elevated atmospheric CO2 level was tested against measurements collected at the FACE (Free Air Enrichment Experiment) site in 1994. Simulated and measured canopy conductances were reduced by about 30% under elevated [CO2] under optimum conditions of water supply. Reductions in latent heat fluxes under elevated instead of ambient [CO2] caused reductions in both simulated and measured seasonal water use of 6% under optimum and 2% under suboptimum irrigation. The soil-plant-atmosphere water transfer scheme proposed here offers several advances in the simulation of land surface interactions. First, the stomatal resistance model minimizes assumptions in existing land surface schemes about the effects of interactions among environmental conditions (radiation, temperature, CO2) upon stomatal behavior. These interactions are resolved in the calculation of CO2 in which processes are already well understood.